In the era of TV and Internet ,I am till intrested in radio circutery and listening radio on SW band , I appreciate your efforts in this subject,Love from INDIA. I have worked in TV industry 45 yr. as sr. Engr. but intrest in radio circutery is my passion.
Thanks Barry, I know it, you have attended me about that... That is why I am, in this video, hesitating a little bit about it, when talking. Having your earlier comment in mind...
It seems that practically every electret mic circuit I come across biases only to the high side which I have learned is considered bad practice. Do you know why that is?
Please elaborate on your question. What do you mean with "the high side" and (thus) why could that be "bad practice", when it biases (?) in that way. What does that "biasing" mean, in your case? And what are the properties of that "biasing"? Also in regard to what that means, when you say it is "considered as bad practice". Thanks for your comment and question. 16 July 2024.
@@radiofun232 Sorry if I wasn't clear. See 6:30. There is a 330k resistor pulling up the base of the first transistor. It is providing a positive bias. On the second stage, the base of the darlington also has a pullup resistor (the two 1m2 resistors). Quite often, when transistors are biased, it is biased both positive (as you are showing), but also negative (to ground) through another resistor. In the book "The Art of Electronics", they would consider it a "bad" biasing circuit if it doesn't have both pull up and pull down resistors. Yet practically every microphone circuit I see, does it the same way as you show in your schematic. I'm just wondering if there is a good reason for that. Thanks.
@@Enigma758 That can be explained. The grounded emitter stage has a high voltage amplification. By its properties. More on the www. Yes, often you see in these G-E setups the following things: a voltage divider that biases the NPN transistor. It goes between (+) and (-) and consists of 2 resistors, where the node goes to the base of the transistor. Be it NPN or PNP. They need to set the transistor to a certain biasing, so that it can amplify audio signals properly. That type of biasing is, like you know, made to amplify audio signals (say sine waves) and serves the way that audio signals are amplified. It must be pure sine wave amplification. No overdrive or non-linear amplification, because that will mean clipping and audio distortion. In such a case (healthy biasing): often (say) a 100 N -470 N cap into the base and a 100 N-470N cap out, signal taken out at the collector, opposite to ground, here mass-minus. That is linear (say audio) amplification and how that audio signals, music, speech, (20 Hz-20 KC) is amplified properly. The sine wave + and the sine wave - part of the wave can be set to be amplified properly. That is set via the voltage divider/biasing. You can allign that very properly in all kinds of G-E amplifiers, made with 1 transistor, by using a 25K potentiometer, node tot he base. And at the upper electrode of that potentiometer (in case of a NPN transistor) a resistor of 1 K to the (+), to prevent destruction of the transistor, when turning the potmeter to its highest position when searching for the right bias. Say that are the “essentials” of biasing a transistor to a working point where it is able to amplify audio signals properly/pure. This does not refer to, like you know, a “switch circuit”, where the base of the transistor gets such a high current, that we have a saturation current between the Collector and the Emitter, driving a relay or whatever in the C-E lead. In this case of a 3 stage audio (!) amplifier on 3 Volt (that is crucial) we use the 3 transistors in such a way that they have their maximum current amplification, connecting the emitter directly to the (-) minus. In a G-E circuit it means that the current amplification of the transistors is set to their maximum and also that there is no frequency dependent element (R-C) in the emitter lead (your question). So these transistors are set to their “bare” amplification properties. That is necessary, because we only have 3 Volts, and, like I explained in an earlier video, link is in the textbox, we only have (say) 2 Volts effective to “do” something, thus say drive a headphone of say 32 Ohm or whatever. With (say) only 2 effective Volts and 10 mA out of the battery that only means 2 Volts x 10 mA = 20 milliwatt to the headphone. That is say enough in this case. Hope this helps & thanks for your comment. 16 July 2024.
I see you did a lot of work. It is metal case, batteries and three transistors. But BUT you have 55db SNR microphone capsule. It is rubbish capsule. Thank you.
I can say that it works very good, listening with it to a UA-cam video, also with a low noise. 16 July 2024.
Thanks for explaining electret microphones. I never understood them!
In the era of TV and Internet ,I am till intrested in radio circutery and listening radio on SW band , I appreciate your efforts in this subject,Love from INDIA. I have worked in TV industry 45 yr. as sr. Engr. but intrest in radio circutery is my passion.
Thanks for your comment.
👍Thank you sir.
Thumbs 👍
Thanks.
We call "multiplex" wood, Plywood in the States. 😁
Thanks Barry, I know it, you have attended me about that... That is why I am, in this video, hesitating a little bit about it, when talking. Having your earlier comment in mind...
@@radiofun232
Oh, It's okay. I just wanted to give you the US word for that wood product. 😁
It seems that practically every electret mic circuit I come across biases only to the high side which I have learned is considered bad practice. Do you know why that is?
Please elaborate on your question. What do you mean with "the high side" and (thus) why could that be "bad practice", when it biases (?) in that way. What does that "biasing" mean, in your case? And what are the properties of that "biasing"? Also in regard to what that means, when you say it is "considered as bad practice". Thanks for your comment and question. 16 July 2024.
@@radiofun232 Sorry if I wasn't clear. See 6:30. There is a 330k resistor pulling up the base of the first transistor. It is providing a positive bias. On the second stage, the base of the darlington also has a pullup resistor (the two 1m2 resistors). Quite often, when transistors are biased, it is biased both positive (as you are showing), but also negative (to ground) through another resistor. In the book "The Art of Electronics", they would consider it a "bad" biasing circuit if it doesn't have both pull up and pull down resistors. Yet practically every microphone circuit I see, does it the same way as you show in your schematic. I'm just wondering if there is a good reason for that. Thanks.
@@Enigma758 That can be explained. The grounded emitter stage has a high voltage amplification. By its properties. More on the www. Yes, often you see in these G-E setups the following things: a voltage divider that biases the NPN transistor. It goes between (+) and (-) and consists of 2 resistors, where the node goes to the base of the transistor. Be it NPN or PNP. They need to set the transistor to a certain biasing, so that it can amplify audio signals properly. That type of biasing is, like you know, made to amplify audio signals (say sine waves) and serves the way that audio signals are amplified. It must be pure sine wave amplification. No overdrive or non-linear amplification, because that will mean clipping and audio distortion. In such a case (healthy biasing): often (say) a 100 N -470 N cap into the base and a 100 N-470N cap out, signal taken out at the collector, opposite to ground, here mass-minus. That is linear (say audio) amplification and how that audio signals, music, speech, (20 Hz-20 KC) is amplified properly. The sine wave + and the sine wave - part of the wave can be set to be amplified properly. That is set via the voltage divider/biasing. You can allign that very properly in all kinds of G-E amplifiers, made with 1 transistor, by using a 25K potentiometer, node tot he base. And at the upper electrode of that potentiometer (in case of a NPN transistor) a resistor of 1 K to the (+), to prevent destruction of the transistor, when turning the potmeter to its highest position when searching for the right bias. Say that are the “essentials” of biasing a transistor to a working point where it is able to amplify audio signals properly/pure. This does not refer to, like you know, a “switch circuit”, where the base of the transistor gets such a high current, that we have a saturation current between the Collector and the Emitter, driving a relay or whatever in the C-E lead.
In this case of a 3 stage audio (!) amplifier on 3 Volt (that is crucial) we use the 3 transistors in such a way that they have their maximum current amplification, connecting the emitter directly to the (-) minus.
In a G-E circuit it means that the current amplification of the transistors is set to their maximum and also that there is no frequency dependent element (R-C) in the emitter lead (your question). So these transistors are set to their “bare” amplification properties.
That is necessary, because we only have 3 Volts, and, like I explained in an earlier video, link is in the textbox, we only have (say) 2 Volts effective to “do” something, thus say drive a headphone of say 32 Ohm or whatever. With (say) only 2 effective Volts and 10 mA out of the battery that only means 2 Volts x 10 mA = 20 milliwatt to the headphone. That is say enough in this case. Hope this helps & thanks for your comment. 16 July 2024.
I see you did a lot of work. It is metal case, batteries and three transistors. But BUT you have 55db SNR microphone capsule. It is rubbish capsule. Thank you.
OK, nothing is perfect...And everyone can use another capsule.